Hi there! Provided you’ve got “GraphEditor” as a module dependency in your .Build.cs file, you should be able to see, and #include "ConnectionDrawingPolicy.h" from anywhere inside your module. Is this not the case?
The header itself resides inside the Public folder (not Private, as stated in the question) so it should be exposed and visible. FConnectionDrawingPolicy is also marked as GRAPHEDITOR_API which means it is safe to be extended from by clients.
Could you elaborate on your module structure and possibly provide us with a snippet of source code?